While I see what your problem is, to be honest it's a bit of a non-issue in my opinion. It's not a social club, you're there to learn a martial art - if the class ends up more like a social club than a martial arts lesson, then you'll probably want to find a new school.
Edit: I just realised that I'm probably biased in my viewpoint of disregarding the social aspect. As an ethnic minority, I'm so used to being outnumbered in a different way that I don't really pay much attention to the gender balance.
While this is probably where the groin guard comes in useful, I think it'd depend on what your personality is like. Aggressive physical action pretty much shuts down any libido I have.
While I have sparred against some very attractive women, I quickly realised that it would be sexist and disrespectful of me to treat them any different - they're there to train, not to get drooled over. If you want to try and hit on them, do so after the class.
About the only time I 'go easy' on my partner is when there's a significant skill/physical difference or they ask me to - I ended up once against one poor girl who about half my weight, 6" shorter and had only started kickboxing that term (I had been training for about 4 years by that point). I just didn't have the heart to spar properly against her.